Acne is an inflammatory disease occurring in hair follicles in skin and sebaceous glands. Internal causes of acne include secretion of sebum and disorders in ingredients of sebum, caused by endocrine actions such as a change in hormones including cortisol secreted by stress or progesterone related to menstruation, and imperforation in sebaceous glands and hair follicles caused by hypersecretion of sebum.
External causes of acne include an increase in sebum, which causes stimulation factors of Propionibacterium acnes living in sebaceous glands to stimulate the epithelial walls of hair follicles so that the corneous layers of inner surfaces of the epithelium are thickened, resulting in imperforation caused by abnormal keratinization of hair follicles and a decrease in oxygen introduction into hair follicles. Such conditions are favorable to the growth of anaerobic P. acnes, the cause of acne, and thus accelerate the growth of P. acnes in lesions of acne.
Meanwhile, approximately 0.05-0.4 mg/cm2 of sebum always exists on the skin surface. Such sebum is produced through two different paths: sebaceous lipids such as triglycerides, squalane or wax esters, and epidermal lipids produced between epithelial cells, such as phospholipids or, cholesterols.
Sebum is combined with water, such as sweat, to form a thin sebum layer in the form of weak acidic emulsion on the skin surface, so that it functions as a luburicant on the skin surface, prevents introduction of external foreign materials and evaporation of water in the skin, and protects skin from various types of physical and chemical irritations.
However, it is reported that excessive sebum causes seborrheic dermatitis, such as acne, and lipid peroxides produced by UV rays are one of the causes of skin irritation.